397 research outputs found
Robust D-wave Pairing Correlations in a Hole-Doped Spin-Fermion Model for Cuprates
Pairing Correlations are studied numerically in the hole-doped spin-fermion
model for cuprates. Simulations performed on up to 12x12 clusters provide
robust indications of D-wave superconductivity away from half-filling. The
pairing correlations are the strongest in the direction perpendicular to the
dynamic stripe-like inhomogeneities that appear in the ground state at some
densities. An optimal doping, where the correlations reach a maximum value, was
observed at about 25% doping, in qualitative agreement with hight T_{c}
cuprates' experiments. On the other hand, pairing correlations are suppressed
by static stripe inhomogeneities.Comment: 4 pages, 4 figure
Pseudogap Formation in Models for Manganites
The density-of-states (DOS) and one-particle spectral function of the one- and two-orbital models for manganites, the latter with
Jahn-Teller phonons, are evaluated using Monte Carlo techniques. Unexpectedly
robust pseudogap (PG) features were found at low- and
intermediate-temperatures, particularly at or near regimes where
phase-separation occurs as 0. The PG follows the chemical potential
and it is caused by the formation of ferromagnetic metallic clusters in an
insulating background. It is argued that PG formation should be generic of
mixed-phase regimes. The results are in good agreement with recent
photoemission experiments for .Comment: Accepted for publication in Phys. Rev. Lett., 4 pages, Revtex, with 4
figures embedde
One-Particle Anomalous Excitations of Gutzwiller Projected BCS Superconductors and Bogoliubov Quasi-Particle Characteristics
Low-lying one-particle anomalous excitations are studied for Gutzwiller
projected strongly correlated BCS states. It is found that the one-particle
anomalous excitations are highly coherent, and the numerically calculated
spectrum can be reproduced quantitatively by a renormalized BCS theory, thus
strongly indicating that the nature of low-lying excitations described by the
projected BCS states is essentially understood within a renormalized Bogoliubov
quasi-particle picture. This finding resembles a well known fact that a
Gutzwiller projected Fermi gas is a Fermi liquid. The present results are
consistent with numerically exact calculations of the two-dimensional t-J model
as well as recent photoemission experiments on high-T_{\rm C} cuprate
superconductors.Comment: 5 pages, 3 figures, accepted for publication in Phys. Rev. B 74,
180504(R) (2006
Charge transfer in heterostructures of strongly correlated materials
In this manuscript, recent theoretical investigations by the authors in the
area of oxide multilayers are briefly reviewed. The calculations were carried
out using model Hamiltonians and a variety of non-perturbative techniques.
Moreover, new results are also included here. They correspond to the generation
of a metallic state by mixing insulators in a multilayer geometry, using the
Hubbard and Double Exchange models. For the latter, the resulting metallic
state is also ferromagnetic. This illustrates how electron or hole doping via
transfer of charge in multilayers can lead to the study of phase diagrams of
transition metal oxides in the clean limit. Currently, these phase diagrams are
much affected by the disordering standard chemical doping procedure, which
introduces quenched disorder in the material.Comment: 14 pages, 9 figures. Invited article for a special issue of JPCM on
Metal Oxide Thin Films; minor changes in the tex
Resistivity of Mixed-Phase Manganites
The resistivity of manganites is studied using a
random-resistor-network, based on phase-separation between metallic and
insulating domains. When percolation occurs, both as chemical composition and
temperature vary, results in good agreement with experiments are obtained.
Similar conclusions are reached using quantum calculations and microscopic
considerations. Above the Curie temperature, it is argued that ferromagnetic
clusters should exist in Mn-oxides. Small magnetic fields induce large
changes and a bad-metal state with (disconnected) insulating
domains.Comment: 4 pages, 4 eps figure
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